Method of fabricating curved tubing and product thereof

ABSTRACT

A method of bending a metal tube including providing an elongated unitary multiwalled metal tube having an internally disposed elongated web with transverse ends connected to generally opposed walls of the tube and dividing the internal hollow into generally equal sections. The tube is then bent in a direction generally perpendicular to the elongated web to establish a predetermined tube curvature. The tube may be of generally rectangular cross sectional configuration with the tube curvature (ratio of height to width) being about 22 to 50 percent. The web will preferably be positioned at or adjacent the neutral axis of the tube in bending. The rectangular tube sidewalls preferably have a maximum wall thickness at or adjacent their upper and lower extremities and a minimum wall thickness at or adjacent the middle thereof. The curved tube product of the above method devoid of appreciable undesired wall collapse resulting from the bending operation.

United States Patent [191 Vance 1 May 27, 1975 METHOD OF FABRICATINGCURVED TUBING AND PRODUCT THEREOF [76] Inventor: Lawrence T. Vance, 1429Little Whale Neck Rd., Merrick, NY. 1 l566 [22] Filed: Nov. 21, 1973[21] Appl. No.: 417,890

Primary Examiner-Lowell A. Larson Attorney, Agent, or FirmArnold B.Silverman [57] ABSTRACT A method of bending a metal tube includingproviding an elongated unitary multiwalled metal tube having aninternally disposed elongated web with transverse ends connected togenerally opposed walls of the tube and dividing the internal hollowinto generally equal sections. The tube is then bent in a directiongenerally perpendicular to the elongated web to establish apredetermined tube curvature. The tube may be of generally rectangularcross sectional configuration with the tube curvature (ratio of heightto width) being about 22 to 50 percent. The web will preferably bepositioned at or adjacent the neutral axis of the tube in bending. Therectangular tube sidewalls preferably have a maximum wall thickness ator adjacent their upper and lower extremities and a minimum wallthickness at or adjacent the middle thereof.

The curved tube product of the above method devoid of appreciableundesired wall collapse resulting from the bending operation.

10 Claims, 7 Drawing Figures PATENTEDi-MYN 1975 3,885,412

SHEET 1 FIG. 3.

vm'mmsm SHEET FIG. Z

METHOD OF FABRICATING CURVED TUBING AND PRODUCT THEREOF BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates to animproved method of bending a multiwalled metal tube into a curved shapeand the product thereof and, more specifically. this invention relatesto such a method and product wherein appreciable undesired distortion ofone or more tube walls during bending is resisted.

2. Description of the Prior Art In prior art practices where it has beennecessary to bend a hollow multiwalled metal tubular product, difficultyhas frequently been encountered as a result of undesired, inherentinward collapse of one or more walls of the tube during the bendingoperation. See generally U.S. Pat. Nos. l,9l3,4l7 and 3,081,795. As suchtubular products are frequently needed or desired in' numerous end useenvironments, including architectural uses, it has been known to adoptpractices which will resist undesired inward deformation of one or morewalls of such tubular products when they are bent along a curved path.For example, it has been known to fill the interior hollow of the tubewith sand, shot or similar materials in order to provide internalsupport during bending. Such systems are undesirable as they require theuse of additional material not required in the end products and theadditional labor involved in introducing and removing the supportmaterial.

In general, such problems have not been encountered in the bending ofcylindrical tubing in a curved path as such tubing possesses symmetryabout the circumference and ready access for uniform positioning ofexternal rollers is permitted. While it has been suggested to providevarious forms of integral support for such tubes, such supports have notbeen necessitated by problems such as those which arise in multiwalledtubes. See generally U.S. Pat. Nos. 1,930,285, 2,196,708 and 3,110,754.

U.S. Pat. No. 3,105,522 discloses a multipiece tube having a divider weband being adapted to be bent in a direction aligned with the orientationof the divider web. The tube is adapted to withstand internal pressuresgenerated by the passage of a coolant material therethrough. Bending ofthis tube is said to be facilitated by a reduction in tube width atcertain regions, with the divider web not serving any particularfunction during the fabricating stages.

There remains, therefore, a very substantial need for a method whichwill effectively provide desired predetermined curved bending of a metalmultiwalled tubular product while resisting undesired wall deformationduring the bending operation. There remains the further need for such aprocess wherein the desired bending may be effected without the use ofinefficient and expensive tube filling and emptying processes of theprior art.

SUMMARY OF THE INVENTION The above-described problems have been solvedby the method of the present invention and the product resulting fromthe practice of such method.

In the present invention an elongated unitary multiwalled metal tube isprovided with an internally disposed elongated web having transverseedges or ends connected to generally opposed walls of the tube anddividing the internal hollow into generally equal sections. The tube isthen bent into a predetermined curvature in a direction generallyperpendicular to the elongated web. Bending is preferably effected toestablish a curvature of about 22 to 50 percent. In a multiwalled tubeof rectangular configuration the sidewalls to which the elongated web isattached are preferably of non-uniform thickness with the sidewallshaving a maximum wall thickness adjacent the upper and lower extremitiesthereof and a minimum thickness generally midway therebetween in theregion where the web is connected thereto. Bending is preferablyeffected progressively in order to establish a uniform curvature ofabout 22 to 50 percent. The tube may be provided with either anelongated web which is formed as a unit with the tube as by extrusionor, in the alternative, it may be provided with a web which isseparately formed and subsequently joined to the tube.

The product of the method of this invention will have the desired degreeof curvature, will preferably be substantially devoid of meaningfulundesired tube wall deformation resulting from the bending operation andwill generally preserve the original cross sectional configuration ofthe tube.

It is an object of this invention to provide a method of bending aunitary metal multiwalled tube along a predetermined path in order toprovide a predetermined curvature without meaningful undesired tube walldeformation.

It is another object of this invention to provide such a method and theproduct thereof wherein the need to employ filler material such as sand,shot and the like is eliminated.

It is a further object of this invention to provide such a method andthe product thereof wherein the multiwalled tube may be progressivelycurved by means of conventional bending techniques and apparatus withthe avoidance of undesired tube wall deformation being provided by meansintegral with the workpiece.

It is yet another object of this invention to provide such a method andproduct which may be adopted economically and readily without requiringmajor changes in equipment and procedures for producing the workpiece.

These and other objects of the invention will be more fully understoodfrom the following description of the invention, on reference to theillustrations appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view ofan elongated multiwalled metal tube of a type employed in thisinventlon;

FIG. 2 is a cross sectional view of the metal tube of FIG. 1 takenthrough 2-2 of FIG. 1;

FIG. 3 is a front elevational view of the tube of FIG. 1 afterfabrication in accordance with this invention;

FIG. 4 is a cross sectional view of an elongated multiwalled metal tubeshowing a modified form of the invention;

FIG. 5 is a cross sectional illustration of a modified form of webmember adapted for use with the tube'of FIG. 4;

FIG. 6 is a partially schematic representation of a form of apparatususable in the practice of this invention; and

FIG. 7 is a cross sectional view of the apparatus of FIG. 6 takenthrough 7-7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As used herein, the termmultiwalled as employed in describing a metal tube shall refer to a tubehaving a non-cylindrical cross sectional configuration and having across sectional configuration defined by three or more wall sectionswhich cooperate to define the internal hollow of the tube. The termwould encompass, but not be limited to, metal tubes having triangular,rectangular, pentagonal and hexagonal cross sectional configurations.The term, in the preferred form of the invention, shall refer to tubeshaving a cross sectional configuration in the shape of a polygon of nsides wherein n equals three to ten.

Referring now more specifically to FIGS. 1 and 2, there is shown anelongated seamless multiwalled metal tube 2 which may be of any desiredlength and preferably has a substantially uniform cross sectionalconfiguration throughout its length. In the particular form shown, thetube 2 is of generally rectangular configuration having an upper wall 4,a lower wall 6 and a pair of sidewalls 8, 10. It will be seen that thesidewalls 8, are of varying thickness. The sidewalls 8, 10 have amaximum wall thickness generally in the regions of the upper and lowerextremities 8a, 8b, 10a, 10b and have a minimum wall thickness generallyin the regions 80, 10c midway therebetween. It is noted that there ispreferably a generally uniform taper between the extremities 8a, 8b,10a, 10b and the regions 80, 10c, respectively, for reasons which willbe stated below. It is also noted that upper wall 4 and lower wall 6have varying wall thicknesses with the maximum wall thickness beingadjacent transverse ends thereof and the minimum thickness beinggenerally midway therebetween.

In the particular form of tube shown, the profile is adapted for use inarchitectural systems, such as by use as a skylight mullion. It will,therefore, be noted that sidewall 8 has a flange 16 which is integrallyformed and extends outwardly and then upwardly in order to cooperatewith another portion of the sidewall 8 in defining moisture receivinggutter 18. Similarly, flange 20 of sidewall 10 extends outwardly andthen upwardly and cooperates with another portion of sidewall 10 todefine upwardly open moisture receiving gutter 22. The upper wall 4 isprovided with channel 24 which defines screw receiving slot 26. Upperwall 4 also defines a pair of upwardly open gasket receiving recesses28, 30.

Referring now to FIGS. 2 and 3, the bending process of the presentinvention will now be considered in greater detail. FIG. 3 illustratesthe seamless tube 2 of FIG. 1 after bending to a desired degree ofcurvature has been accomplished. As used herein a reference to curvatureor words of similar import shall refer to the ratio of height H to widthW of a curved tube wherein height H is measured between the level of thelongitudinal axis at the tube ends and the longitudinal axis at thecenter of the tube and width W is measured between the tube ends at thelongitudinal axis. As is shown in FIG. 2, tube 2 has a generallycentrally located integrally formed elongated web 40 which has itstransverse ends connected to sidewalls 8, 10. Web 40 is preferablypositioned generally parallel to upper wall 4 and lower wall 6 and isdisposed generally midway therebetween. Web 40 serves to divide theinterior hollow of the tube 2 into two generally equal sections 42, 44.Web 40 is preferably substantially continuous and substantiallycoextensive with tube 2. During the bending operation of the presentinvention, bending will be effected in a direction generallyperpendicular to web 40. As a result, the portion of tube 2 disposed ata level above web 40 will be placed in tension during the bendingoperation and the portion of the tube disposed below the level of web 40will be placed in compression during the bending operation. The web 40will preferably be disposed generally along the neutral axis, i.e., willnot be under appreciable tension or compression during the bendingoperation.

In general, it will be preferred to provide a web 40 which has a wallthickness less than the maximum wall thickness of sidewalls 8, l0 andpreferably in the range of about 20 to 80 percent of the maximum wallthickness of sidewalls 8, 10. In general, great wall thickness of web 40is not required in order to provide the strength needed for the processof the invention and where the web 40 is provided as an integralextruded portion of the tube 2, it may be made in the minimum thicknesswhich the state of the extrusion art permits. This serves to reducemetal costs and product weight. In the preferred practice of theinvention, bending will be effected to establish a generally uniformtube curvature of about 22 to 50 percent.

It has been found that the normal tendency for tube sidewalls tocollapse inwardly during bending can be resisted by providing theirregular sidewall thickness described above. Providing theabove-described taper may result in the sidewalls 8, 10 experiencingsome outward distortion during the bending operation. It has been foundthat positioning the web 40 along or adjacent to the sector of maximumexpected bending will result in resisting such undesired distortion. Tothe extent to which the sidewalls 8, 10 would normally deformtransversely inwardly during the bending operation, the web 40 isbelieved to serve as a column which resists such deformation by itscompressive strength and the extent to which outward deformation wouldnormally result from bending, the tensile strength of the web 40 resistssuch undesired distortion. As a result, one may effectively produce thedesired curved tube by means of the present invention withoutexperiencing undesired deformation of one or more tube walls.

Referring now to FIGS. 4 and 5 another embodiment of the invention willbe considered. While in general the tube may advantageously be formed asa unitary seamless unit of a suitable metal such as aluminum or bronze,for example, by an extrusion process and web 40 may be formed duringsuch an extrusion process, an alternate approach may be taken ifdesired. While the embodiment wherein the web is formed integrallyduring the extrusion process is preferred, if desired, the embodimentshown in FIGS. 4 and 5 may be employed as an effective alternative. Asis shown in FIG..4, tube 50 is of generally rectangular configurationhaving an upper wall 52, a lower wall 54 amd a pair of sidewalls 56, 58.Sidewall 56 is provided with a moisture receiving gutter 60 which isdefined by flange 62 in cooperation with a portion of sidewall 56.Similarly, flange 64 cooperates with a portion of sidewall 58 to definegutter 66. It will be appreciated that gutters 60, 66 may be provided inany desired elevation along sidewalls 56,

58. It is noted that sidewall 56 has a pair of inwardly projectingflanges 70, 72 which cooperate to define re stricted throat recess 74.Similarly, sidewall 58 has inwardly directed flanges 76, 78 whichcooperate to define restricted throat recess 80. As is shown in FIG. 5,a web 82 has a pair of generally T-shaped ends 84, 86. Web 82, which ispreferably substantially, continuous and substantially coextensive withtube 50, is adapted to be secured to tube 50 by axialjinsertion of theweb 82 into the tube interior in such fashion that end 84 is receivedwithin recess 74 and end 86 is received within recess 80. While .thisembodiment does not provide the advantage of automatic creation andconnection of the web member within the tube interior, there may becertain uses for which such an approach may advantageously be employed.

Referring now to FIGS. 6 and 7, one form of bending operation which maybe employed in the present invention will now be considered. As is shownin FIG. 6, a tube 90 is moving through a group of roller dies 92, 94, 96in the direction indicated by the arrow. The relative positions of thethree dies 92, 94, 96 will determine the degree of curvature imparted tothe tube 90 as it moves progressively through the dies. In the formshown roller 94 is a driver die, roller 92 is a driven die and roller 96is an idler die which is adjustable in the direction indicated by thedouble arrow. All of the rollers rotate in the directions indicated bythe arrows.

As is shown in FIG. 7, the roller dies 92, 94 have configurations whichwill permit ready engagement of the tube 90 without undesireddeformation thereof during the bending operation. It is also noted thatthe web 98 disposed within the tube 90 as described above will serve toresist undesired meaningful inward or outward deformation of the tubesidewalls. In the form shown, a suitable power source will cause gear100 to drive roller 94 and through the operative connection with gear102 to drive roller 92. A suitable thrust collar 104 is provided.

While the present invention is adapted for use on a wide range of metalsemployed in tube construction, it will generally be most advantageous toemploy the method on metal tubes of a gauge and material designed forboth structural and decorative architectural uses. For example, metaltubes made out of extruded aluminum or bronze may frequently beadvantageously employed in the practice of the invention. Aluminumalloys of the 6063 and 6061 types are exemplary of those which may beemployed. In general, such tubes will have a wall thickness within thezones of minimum thickness SC, 100 in the range of about 0.080 to 0.250inch.

While for simplicity of description above, reference has been made to arectangular multiwalled tube, it will be appreciated that the inventionis applicable to other multiwalled tubes. In uses where the tube hasmore than four walls, the reference to the transverse ends of the webbeing connected to generally opposed walls shall be deemed to includeconnections between an end of the web and a point where two adjacentwalls meet. Also, while it is preferred that the web be positioned onthe neutral axis of the tube, the web may be displaced from this neutralaxis a distance which does not result in excessive undesired tube walldeformation during the bending operation. Finally, while for convenienceof description herein there has been reference to a unitary web, it willbe appreciated that, although not preferred, twoor'more webs whichfunction to provide the benefits of the unitary web may be substitutedtherefor if desired and such substitution shall be deemed to beencompassed within the scope of this invention.

While for convenience of description herein reference has been made tovarious relative directions such as upper." lower," side" and the like,these words are not, in the absence of express indications to thecontrary, to be deemed limitations on theinvention.

It will, therefore. be appreciated that the method and product of thepresent invention provide for efficient bending of a multiwalled metaltube along a predetermined curved path, while avoiding undesiredmeaningful-tube wall deformation during bending. The general originalcross sectional configuration of the tube can be preserved duringbending. This is accomplished in an economical fashion without requiringmeaningful mod ification to bending equipment and techniques and withoutrequiring the use of inefficient prior art tube filler material, such assand and shot. The method employs means integral with the workpiece toeffect such curved bending, either uniformly or nonuniformly, withoutundesired wall distortion and permits advantageous use of modern metalextrusion techniques in creating the workpiece.

Whereas particular embodiments of the invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details may be made withoutdeparting from the invention as defined in the appended claims.

I claim:

1. A method of bending a metal tube comprising providing an elongatedunitary multiwalled seamless metal tube,

providing said elongated metal tube with an internally disposedelongated web having transverse ends connected to generally opposedWalls of said tube and dividing the internal hollow into two generallyequal sections, and

bending said tube in a direction generally perpendicular to saidelongated web to establish a predetermined tube curvature.

2. The method of claim 1 including said multiwalled metal tube having across sectional configuration in the shape of a polygon of three to tensides.

3. The method of claim 2 including bending said tube progressively bypassing it through a series of roller dies to establish a curvature ofabout 22 to 50 percent.

4. The method of claim 3 including providing said tube as a tube with agenerally rectangular configuration defined by an upper wall, a lowerwall and a pair of spaced sidewalls, and

establishing said elongated web generally parallel to and generallymidway between said upper and lower walls.

5. The method of claim 4 including providing said sidewalls with amaximum wall thickness at or adjacent the upper and lower extremitiesthereof and a minimum thickness at or adjacent the middle thereof.

6. The method of claim 5 including providing said sidewalls with agenerally uniform taper extending generally from the upper and lowerextremities thereof toward the middle thereof.

7. The method of claim 4 including from said tube with flanges at oradjacent the transverse edges thereof,

providing said tube sidewalls with inwardly projecting flanges definingrecesses for receiving said web flanges, and

securing said web to said sidewalls by introducing said web flanges intosaid sidewall flanges.

10.,The method of claim 4 including providing said sidewalls withexteriorly disposed generally outwardly and upwardly directed flangeswhich cooperate with other portions of said sidewalls to define moisturereceiving gutters.

1. A method of bending a metal tube comprising providing an elongatedunitary multiwalled seamless metal tube, providing said elongated metaltube with an internally disposed elongated web having transverse endsconnected to generally opposed walls of said tube and dividing theinternal hollow into two generally equal sections, and bending said tubein a direction generally perpendicular to said elongated web toestablish a predetermined tube curvature.
 2. The method of claim 1including said multiwalled metal tube having a cross sectionalconfiguration in the shape of a polygon of three to ten sides.
 3. Themethod of claim 2 including bending said tube progressively by passingit through a series of roller dies to establish a curvature of about 22to 50 percent.
 4. The method of claim 3 including providing said tube asa tube with a generally rectangular configuration defined by an upperwall, a lower wall and a pair of spaced sidewalls, and establishing saidelongated web generally parallel to and generally midway between saidupper and lower walls.
 5. The method of claim 4 including providing saidsidewalls with a maximum wall thickness at or adjacent the upper andlower extremities thereof and a minimum thickness at or adjacent themiddle thereof.
 6. The method of claim 5 including providing saidsidewalls with a generally uniform taper extending generally from theupper and lower extremities thereof toward the middle thereof.
 7. Themethod of claim 4 including providing said upper and lower walls with amaximum wall thickness at or adjacent the transverse outer extremitiesthereof and a minimum thickness generally midway therebetween.
 8. Themethod of claim 4 including forming said elongated seamless metal tubeand said elongated web as a unitary extrusion having generally the samecross sectional configuration throughout its length, and establishingsaid internally disposed web with a wall thickness less than the maximumwall thickness of said tube sidewalls.
 9. The method of claim 4including forming said elongated web as a separate member from said tubewith flanges at or adjacent the transverse edges thereof, providing saidtube sidewalls with inwardly projecting flanges defining recesses forreceiving said web flanges, and securing said web to said sidewalls byintroducing said web flanges into said sidewall flanges.
 10. The methodof claim 4 including providing said sidewalls with exteriorly disposedgenerally outwardly and upwardly directed flanges which cooperate withother portions of said sidewalls to define moisture receiving gutters.